Endogenous dopamine and cyclic events in the fish retina, I: HPLC assay of total content, release, and metabolic turnover during different light/dark cycles.
In this study, we investigated the potency of dopamine for being an intrinsic signal for cyclic events in the fish retina. Dopaminergic activity was measured during different light/dark cycles, during continuous darkness, and during short-term light and dark adaptation within 1 h. During a 12-h light/12-h dark cycle, the total content of endogenous dopamine was high during the dark phase and low during the light phase. The potassium-induced release of endogenous dopamine followed a parallel time course. The concentration of the dopamine breakdown product 3,4-dihydroxyphenylacetic acid (DOPAC), which reflects the endogenous dopaminergic activity, was high during the light phase and low during the dark phase. Similar alterations occurred in accelerated 6-h light/6-h dark cycles, again indicating a strong coupling of dopaminergic activity with light. The cyclic alterations in the total endogenous dopamine content persisted during continuous darkness after an entrainment of the fish to a 12-h light/12-h dark cycle. Although the magnitude of the change was weaker, changes in dopamine content, potassium-induced dopamine release, and DOPAC were also measured during 1 h of light or dark adaptation. During a 1-h period of dark adaptation, the total content of dopamine and the potassium-induced release of endogenous dopamine increased, while DOPAC values decreased. These values changed in the opposite direction during 1 h of light adaptation. Our findings strongly suggest that dopamine is the intrinsic signal for light during both the light and dark phases and during short-term adaptation. Light seems to be the major trigger for dopaminergic activity within the fish retina.(ABSTRACT TRUNCATED AT 250 WORDS)
Kolbinger
W
W
Department of Neurobiology, University of Oldenburg, Federal Republic of Germany.
Kohler
K
K
Oetting
H
H
Weiler
R
R
D015102:3,4-Dihydroxyphenylacetic Acid / Q000378:metabolism; D000818:Animals; D002347:Carps / Q000502:physiology*; D002851:Chromatography, High Pressure Liquid; D002940:Circadian Rhythm; D003624:Darkness; D004298:Dopamine / Q000378:metabolism*; D008027:Light; D010507:Periodicity; D011188:Potassium / Q000494:pharmacology; D012160:Retina / Q000502:physiology*; D013997:Time Factors
D015102:3,4-Dihydroxyphenylacetic Acid; D011188:Potassium; D004298:Dopamine